So you can join them up like this...
First select Format on Measure Values
and from the resulting menu (Pane Tab) Select "Hide and Connect Lines"
I've also attached a version using the single data-source, where I've used a dual axis, and changed aggregation to Avg (although each Month Average is plotted on the 1st of each month, as this is how Tableau [and most other programs] TRUNCate dates to Week, Month...etc).
With regards the dotted lines, unfortunately not "out of the box" with Tableau (there are some workarounds out there but they are quite involved). In the second version I've reduced the transparency and size of the day lines, so it fades into the background, as context ...which I quite like to show Daily noise and higher level trends. With the Blended version, you can use the colour pallets to choose lighter tones for the day level lines.
Hope that helps
TempGraph_sr.twbx 105.7 KB
That's great. Thank you so much.